1. Field of the Invention
The present invention relates to a hydraulic pressure control valve which is provided in a brake system of a vehicle.
2. Description of the Prior Art
Generally, a hydraulic pressure control valve that is provided in a brake system of a vehicle is designed to lower the rate of increase in hydraulic pressure supplied from a master cylinder to a brake cylinder associated with a rear wheel, when the hydraulic pressure exceeds a predetermined level, thereby preventing a locking of the wheel.
One type of conventional hydraulic pressure control valve which has heretofore been arranged to prevent a built-in sealing member from coming off when the control valve is assembled to a vehicle or is reassembled after overhauling, is disclosed in Japanese Utility Model Public Disclosure (KOKAI) No. 63-61373.
Referring to FIG. 1, which illustrates the above-described prior art valve a hydraulic pressure control valve 1 has a body 2 that is provided with a bore having a small-diameter bore portion 4 that is formed at the side which is closer to an inlet port 3, and a sealing member 8 is disposed within an annular groove 7, which is defined between the small-diameter bore portion 4 and a small-diameter portion 6 of a stepped piston 5. The small-diameter bore portion 4 has the diameter at the open end thereof reduced by an annular inward projection 9.
With this structure, the sealing member 8 is prevented from coming out of the groove 7 during the evacuation of air when brake fluid is charged into the brake system, and it is also possible to prevent the sealing member 8 from being pushed out of the groove 7 by the small-diameter portion 6 of the piston 5 when the control valve 1 is reassembled after overhauling.
This conventional hydraulic pressure control valve 1 suffers, however, from the following problems.
The small-diameter bore portion 4 in the body 2, within which the sealing member 8 is disposed, is generally formed by cutting, and this cutting the body 2, process is necessarily complicated in order to form the annular inward projection 9 for preventing the detachment of the sealing member 8. In addition, the inner side of the small-diameter bore portion 4 must be finished to a smooth surface in order to ensure satisfactory sealing properties, and for this cutting operation a special tool must be employed due to the obstruction presented by the projection 9. For these reasons, the equipment costs are high, and the machining time is relatively long. Consequently, productivity in the manufacture of the valve is relatively low accompanied by a rise in production costs.